Along with miniaturization and thinning of electronic devices, surface mount type packages, as electronic components to be provided in electronic devices, have come to be used in many cases. For the packages of such electronic components, there are packages which have substrates mounted with electronic components, such as semiconductor elements, and in which the electronic components resin-sealed. Specifically, there are semiconductor packages such as BOC (Board On Chip).
Further, along with miniaturization and thinning of electronic devices, miniaturization and thinning of electronic components provided in the electronic devices are also in progress. In order to provide electronic devices with multiple functions, it is necessary to increase the number of electronic components to be mounted on the electronic devices. In order to address this need as well, miniaturization and thinning of electronic components are in progress. Moreover, thinning of a substrate configuring a package of electronic components is also being implemented as it is being implemented in the electronic components.
Further, the package of the electronic component as described above has a structure of, for example, bimetal that has a sealing resin and a substrate bonded to each other. Such a package occasionally exhibited deformation such as warpage due to a difference in coefficient of thermal expansion (CTE) between the sealing resin and the substrate. In particular, thinner substrates exhibited warpage more often. Moreover, after implementing resin-sealing only on one side of the substrate, warpage was often identified in the substrate. Taking these into account, it is apparent that when electronic devices are used in an environment where temperature changes greatly, repetitive bending is exhibited due to warpage of the package of the electronic component. Therefore, due to the bending, deterioration such as cracks occurred near the surface of the substrate. Due to the deterioration of the substrate, damage such as disconnection of wiring on the substrate surface occurred.
Further, as a substrate used for a package of electronic components, for example, there is used a printed wiring board which is obtained by forming a circuit plate by partially removing a metal layer such as a metal foil arranged on the surface of a metal-clad laminate. As such a metal-clad laminate, there is a copper-clad laminate using a laminated board described in Patent Document 1, for example.
In Patent Document 1, there is described a laminated board that is formed by lamination by impregnating a bisphenol type epoxy resin composition into a sheet-shaped base material. In the laminated board, a sheet-shaped base material of a center layer is a glass fiber woven cloth, and a sheet-shaped base material of a surface layer is a nonwoven fabric of para-system aramid fiber. According to Patent Document 1, it is disclosed that the laminated board has an effect that surface mounting reliability of a chip component is excellent by making a coefficient of linear expansion of the surface layer close to a coefficient of linear expansion of the chip component to be mounted, and that dimensional shrinkage due to heating can be minimized    Patent Document 1: Japanese Patent Application Publication No. H2-63821